RFR: 8339132: Make DirectCodeBuilder write through without allocating instruction objects

[Chen Liang]

Make `DirectCodeBuilder` write instructions actually directly without allocating extra objects. This speed up a lot of simple Class-File building cases that never go through intermediate transforms.

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Commit messages:
 - Moar fixes
 - More direct code builder

Changes: https://git.openjdk.org/jdk/pull/20738/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20738&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8339132
  Stats: 772 lines in 4 files changed: 719 ins; 25 del; 28 mod
  Patch: https://git.openjdk.org/jdk/pull/20738.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20738/head:pull/20738

PR: https://git.openjdk.org/jdk/pull/20738